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Staving Off Disaster At Oroville

overflow onto the Oroville Dam's emergency spillway
The Oroville Dam on Feb. 11, 2017. Photo by William Croyle, courtesy the California Department of Water Resources.

There is some irony as well as a lot of urgency in this week’s efforts to stave off disaster at California’s giant Oroville Dam.

The now-compromised project, which led authorities to place some 188,000 people under evacuation orders, has been staving off disaster since even before it was completed in 1968. The dam was still far below its final 770-foot height (the tallest in the country) in the winter of 1964, when heavy rain and snow sent the Feather River over its banks. But it was already tall enough to hold back a significant amount of flood water, sparing downstream lives and property.

Gov. Ronald Reagan and many other dignitaries were on hand for Oroville’s dedication in May 1968, just as that year’s winter wet season was ending. They had no way to know that the following autumn would mark the start of one of California’s worst flooding winters on record. The winter of 1968-69 inundated large swaths of the Golden State, from Oregon to the Mexican border. But with all that capacity in a vast new reservoir that was just beginning to fill, the town of Oroville and communities downstream all the way to Sacramento were again spared. At its peak that first season, on January 21, 1969, the river poured 124,000 cubic feet of water into the reservoir every second. The next day reservoir managers boosted the outflow to just under 52,000 cubic feet per second.

Oroville is one of the largest elements in the State Water Project, a massive and controversial undertaking that diverted water from California’s normally moist north to the irrigated farms and fast-growing cities to the south. Oroville’s reservoir was so big that it swallowed a pre-existing dam and reservoir known as Big Bend, whose powerhouse lit the city of Oakland in the 20th century’s first decades.

Without the State Water Project and similar efforts, notably the diversion of water from the Colorado River, California’s rise as the pre-eminent population center of the country could never have happened. There were fewer than 1.5 million Californians in 1900, just before Big Bend was constructed. There were nearly 20 million when Oroville was completed, and there are nearly 39 million today.

Like all of the West, California has long been subject to extreme, multiyear fluctuations in weather. Long droughts are not infrequently followed by destructive floods; years of low snowpack in the mountains can be followed by snowfalls measured in dozens of feet.

A year ago there were high hopes that a strong El Nino would send a parade of storms into California to bust a five-year drought. For the most part, that did not happen; the southern half of the state in particular remained severely parched. But the storms did manage to bring Oroville’s reservoir back to normal seasonal levels as last year’s winter ended.

This year, however, the wet weather did materialize. It did so in January, with a vengeance, after a slow start to the precipitation season. By early February Oroville’s reservoir was approaching its capacity, and managers knew they needed to leave room for runoff from the heavy snowpack that has again accumulated in the high Sierra. They released excess water through the dam’s principal concrete spillway.

On Feb. 8, however, a 150-foot-wide hole developed in the main spillway, forcing operators to shut off the outflow temporarily. The reservoir level kept rising. By Saturday, Pacific Gas and Electric crews scrambled to dismantle power lines and other electrical equipment located near the main spillway, so that they would not be dragged away by potential overflow. That day, water overtopped the secondary, emergency spillway for the first time in the dam’s history. While the emergency spillway did effectively prevent water from overtopping – and potentially eroding – the dam itself, it also dumped water onto an open hillside that eroded quickly and severely.

With both spillways damaged, water managers are left with no appealing choices for the rest of the winter. Allowing big outflows through the main spillway will worsen the damage and, in the worst case scenario, cause the top of the spillway to fail and send a large uncontrolled release downstream. Shutting down that spillway outright could force the lake level to again rise over the top of the emergency spillway, which will only worsen the damage to that channel – and increase the risk that the top of the emergency spillway will totally collapse.

The best dam managers can hope for is that the storms will let up for the balance of the season and a cool spring and summer will allow the upstream snow to melt only gradually, reducing the strain on the dam.

There will be a lot of after-action damage assessment once the crisis has passed, and I suspect a lot of finger-pointing as well. Environmental groups that went to court a decade ago in an unsuccessful effort to have a man-made channel built for the emergency spillway will no doubt point out that they warned of the dangers. Inspectors who gave the regular spillway a clean bill of health earlier in the season will need to explain how and why it failed. There will be a debate about whether the state needs to spend more money maintaining its water infrastructure and over where the money will come from.

But the bigger issue is one that California and many other parts of the country have not yet been willing to face. We are trying to get through the 21st century with a 20th century water management infrastructure that was not designed for the population pressures, the energy needs or – regardless how you evaluate the human impact on climate change – the weather extremes of today’s world. The less we prepare, the more we will have to improvise, as the folks scrambling to save Oroville are discovering.

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